I've been trying to feed my red eyed puffer, Wilhelm, some snails to make sure his teeth don't overgrow. The point of the snails is that crunching the shells will wear down his teeth, right?
The problem is, he doesn't eat them shell and all. He doesn't even try to bite the shell. He just waits until it the snail comes out and then bites its head off.

They're not that big, either. The biggest snails (shell and all) are about the size of the eraser on a pencil. I think that maybe the biggest ones are too big for him to eat whole, but not the smaller ones.
Is it OK that he just eats the soft part of the snail? How can I get him to eat the shell also? He won't bite it once there is no snail inside it.